Telephone-exchange system.



No. 793,941 PATENTED JULY 4, 1905. L LAND TELEPHONE EXCHANGE $ZSTEM.

xPPLwATmI FILED JAN 2a 1903 EMT lblrrncnr r ni'innn statue ICIMVIUNI) LAND, OF GRAND RAPIDS, l\'Il(Jl-ll(l-AN, ASSlGUOlt TU STRUPVIHERU- lARLSON TllGLl lPliONlG MANUFAUTUR NU UOM ANY, F ROCllES'TEli, NEW YORK, A (lURPOPA'llUN OF Nl ll'V Y ORK.

SPECIFICATION forming part of Letters Patent No. 798,9et1, dated July I, 1905. Application filed January 23,1903. Serial No. 1&0200.

Y7? A l line-jack causes the closure of a circuit of delfie it known that l, EDMUND LAND, a citizen creased resistance through one of the coils of ofthe UnitedStates, residingatGrandRapids, the differential relay, the energization due in the county of Kent and State of lVIichigan, to this coil thereby unbalancing' that due to 5 have invented a certain new and useful Imthe other coil, and coneeqi'lently causing an provement in Telephone-Exchange clystems, energization of the relay-core adapted to atof which the following is a toll, clear, concise, tract the relay-armature. The attraction of and exact description, reference being had to the relay-armature opens the circuit through the accompanying drawings, forming a part the line-signal, thereby causing the restora 10 of this specification. tion thereof. One of the two contacts of the My invention relates to telephone-cxehange line spring-jack is normally disconnected from systems, and particularly to systems in which the line, the attraction of the relay-armature, a common source of current located at the i however, serving; to connect this contact, or central exchange isemployed for the purpose in a multiple board the corresponding con- 15 of providing signaling-currents and currents tacts in a series of sections, with one limb of for the operation of the substation telephone the telephone-line. The set of spring-jack apparatus. contacts thus connected with a limb of the The objects of my invention are to provide telephone-line are used for the purpose of an improved telephone system in which the testing the operative condition of the line.

:20 complicated cut-oil mechanism heretofore em- The remaining spring-pick contacts are norployed may be dispensed with and to provide mally connected with the other limb oi? the an improved means for testing the condition telephone-line through a coilof the differential of a subscribers line to see whether or not it relay. The actuation of the relay-armature, is in use. however, serves to provide a short-circuit 2 5 While my invention provides a system of shunt-path around this coil of the relay, theregreat mechanical and electrical simplicity, by providing a telephone-line for conversastill the apparatus is not readily subject to detional purposes between the spring-jack con- :lective operation due to defective line insulatacts and the subscribefis substation which tion or leakage or other conditions giving rise entirely free from serially-included im- 30 to electric; l unbalal'icing of a telephone-line. pedancc.

In accordance with my invention I provide The cord-circuit employed in connection a common form of line signal, such as a drop with my invention is normally and continu- 8o normally serially included in circuit with a ously associated with the common source of subscribci"s telephoneline. There is also current in such a way as to permit the closure 35 normally serially included in this line-circuit of the hereinbefore-mentioned low-resistance a dilferentially-wound cut-oil relay. The two circuit through a relay-coil upon the insertion dil'lerentially-wound coils of this relay are di of the cord connecting-plug within the corrercctly connected in series with each other and sponding line-jack. with one limb of the telephone-line. An ar- Talliiiigrurrcnt is supplied to the substa 4 mature cmltrolled by the energization of the tion through a supervisory relay associated differential relay serves to control the circuit with the cord-circuit, whereby the closure of through the line-signal, this circuit being the substation-circuit causes the energization broken upon the attraction of the relay-arof the supervisory relay toeontrol the opera mature. On account of the diilerential windtion of a suitable supervisory signal associated 45 ing of the cut-oil. relay its core not enertherewith. This supervisory signal may dogized upon the closure of the telephone linesirably be in the form of an incandescentlamp circuit at the suhstatioi'i. The insertion of a tlltptml to be illuminated by a current derived plug of the operatofis cord-circuit within a :from the common source oi current at the con tral station. The attraction of the supervisory relay armature breaks a previouslyclosed circuit through the supervisory signallamp, and as the supervisory lamp is normally serially included in one strand of the cord-circuit the attraction of the supervisory relayarmature also serves to short-circuit the supervisory lamp, thereby decreasing the resistance of the talking-circuit through the cord connecting apparatus.

My invention will be more fully understood by reference to the accompanying drawing, in which I have illustrated two substations, A and B, each connected with the central exchange (1 by means of the telephone-limbs 1 and 2.

The substation apparatus consists of a switch-hook 3, the depression of which, due to the weight of the receiver&, normally closes a circuit for alternating currents between the limbs 1 and 2 through a signal-bell 5 and a condenser 6. Upon the removal of the receiver from the switch-hook an alternative circuit for continuous currents is provided through the transmitter T and the primary 8 of an induction-coil whose secondary 9 is serially included in circuit with the receiver a. The limb 1 leads to the coil 10 of a differentially wound relay 11, whose oppositelywound and serially-connected coil 12 is connected with one pole-for instance, the positive pole o'f the comm on battery 13. The differential relay 11 is shown as provided with two armatures, the armature let serving when in its alternative condition to close a low-rcsistance shunt-circuit about the difi'erential relay-coil 10. The other relay-arniature 15 is permanently connected with the limb 2 of the telephone-line. heu in its normal unattracted condition, this armature closes a connection through the contact 16 and a line drop or signal 17 with the negative pole of the common battery 13. The front contact 18 for the armature 15 is connected with the sleeve-springs 19 19 of the answering-jack 20 and the multiple calling-jacks 21 21. It will be seen that these sleevesprings are normally disconnected from every part of thetelephonecircuit and from ground. The tip-springs 22 of the line-jacks are permanently connected by conductor 23 with the connection of the dilierential relay-coils 10 and 12. The contact 24:, which acts in conjunction with the armature 14 to short-circuit the coil 10, is also permanently connected with the tipsprings 22, whereby the attraction of the armature 14:

causes the closure of a non-inductive connection between the tip-springs 22 and the limb 1 of the telephone-line.

The cord-circuit adapted for use with my invention comprises the answering-plug 25 and the calling-plug 26, both connected by the tip-strands 27 and the sleeve-strands 28 with contact-springs of the ringing and listening key 29, which when actuated in one direction serves to connect the ogerators telephone set 30 in bridge between the strands of the cord circuit and when actuated in the other direction serves to break the connection between the answering and calling plugs and to connect the terminals of the ringing-generator 31 with the conductors leadingto the calling-plug 26. The condenser 32 is serially included in the sleeve-strand of the cord-circuit, while the condenser 33 is serially included in the tip-strand thereof. The tipstrand circuit also normally serially includes the supervisory signal-lamps 34C and It will be seen that the condensers 32 and 33, while serving to inductively connect and relate the two sides of the cord-circuit, serve to conductively insulate the same. ith either side of the sleeve-strand 28 is normally connected a terminal of the supervisory relays 36 and 37, the other terminals of these relays being connected with the negative pole of the battery 13. The supervisory relay-armatures 38 and 39 when in connection with back contacts 10 and 11 serve to connect the negative pole of the battery 13 with the supervisory signal-lamps 3% and'35. When in their attracted positions, the supervisory relay-arn'iatures make connection with front contacts a2 and 43 thereby closing short circuits in shunt of the supervisory signal-lamps 3 1 and 35, respectively.

The operation of my improved system will now be apparent. Upon the removal of the receiver at substation A from its switch-hook a circuit for continuous currents is closed through the transmitter '7, which circuit may be traced from the positive pole of the battery 13 through the differentially-wound coils 12 and 10 of the cut-off relay 11, through the limbs 1 and 2 of the telephone-line to the relay-armature 15, to the back contact 16, through the line-relay 17, to the negative pole of the battery 13. On account of the differential winding of the relay-coils 10 and 12 there is no effective energization of the relaycoil 11. The current flowing through the line-drop, however, causes an energization thereof to give the central operator a linesignal. She thereupon inserts the plug 25 of her cord connecting apparatus within the answering-jack 20, as shown in the drawing. A circuit of decreased resistance may thereupon be traced through the cut-ofi-relay coil, as follows: from the positive pole of battery 13 to the coil 12, through conductor 23, tip-spring 22, the tip of the answering-plug 25, the tipstrand 2'7, through the lamp 3% to the armature 38, to the contactetO, to the negative pole of battery 13. This circuit of decreased resistance causes an unbalancing of the magnetization due to the two coils of the differential relay, whereupon the relay is energized to cause the attraction of the armatures 1 1 and 15. The attraction of the armature 1a causes the closure of a short circuit in shunt of the difsprmding |ine-drop 17. hshed throitigh the supervisory relay 37 upon l the removal oi the receiver at substation ll,

veaoai iercntial relay-coil and connects the tipsprings 22 with the limb 1 ol the telephoneline through a circuit including no inductive resistance or impedance. The attraction of the cut-oil relay-armature causes a break in the circuit through the line-drop betweei'i the armature and the contact to. At the same time the connection between the armature 15 and its trout contact 155 closes a direct noninductive circuit between the limb 2 of the tele hone-line and the sleeve-contacts 19 ot' the spring-jacks 20 and 21. The receiver at substation A being removed from its switchhook permits the l'low of current through a circuit which may be traced as follows: from the positive pole oi the battery 13, through the coil i2 of the dilierential relay to the con d actor 22:), to contact 24;, to armature let, to limb ,l. of the telephone-line, through the transmitter at substation A to limb 2 ol the telephone-line, to armature l5 oi? the dil'ij'erential relay, to contact 18, to sleeve-swing it) of the answering jack 20, to the sleeve-contact of the answering-plug 25 to sleeve-strands 2S, and through the supervisory relay 36 to the negative pole of the battery 13. The consequent energization of the supervisory relay 36 causes the attraction of its armatures 38, \VllGlCl1])()Ii the supply of battery-current to the supervisory signal-lamp EH is cut oil' at the sai'ne time the connection between the supervisory relay-armature 38 and its :tront contact 4-2 closes a loiva'esistance shuntcireuit around the lamp St. The necessary ei'iergization oi. the coil 12 is maintained by the [low of current through the circuit-supplying talkingcurrent to the substation A, this circuit including the battery 13, the coil 12, the limbs l and 2 oi the tele1:)hone-line, the armature 15 and contact 18, the sleeve-strands 2S, and the relay 3b. The operator upon ascertaining in. the usual way that the subscriber at substation it desires connnunication with the subscriber at substation H inserts her calling-plug 26 within a line-jack 21' corresponding to the desired substation A circuit similar to that previously traced for the apparatus associated with the substation llt may be traced through the coil 12 ot the called-snbscril; ers cut-oil relay, where-- upon the cut-oil relay is actuated to immedi' ately break the connection with the corre- A circuit is estab- Wherengmn the relay-armature is attracted to eatihguish the lamp b5 and providea short tircnit l'or voice-currents through the cord strand ill The condensers 32 and 33, as above pointed onascrvc to corulnctirely insulate the two sides of the cord-circuit whereby each 01 the supervisory relays 36 and 37 is positively and absolutely controlled by the correspmuling substation a n iaratus connected therewith.

The tn ieratofis busy test lo' ascertaining whether or not a desired subscribe1."s line is in operation attained by the use 01 my improved system as follows: The tip of a calling-plug 26 is charged with negative current from the battery 13 through the back contact 4L1, the armature 3i), and the supervisory signal-lainp 35. When a callei|-subseribe1"sline is in use, the corresponding cut-oil? relay will have attracted its armatures l iand 15 to their alternate posi ti on, thereby con nectii'ig the linelimb 2 directly with the thimbles l9 oi the corresponding spring -jacks. illhus all the thimbles in the switchboard-sections corresponding with the substation Ill. for instance, are connected to the circuit through which current is supplied to the sulistatiolrtransmitters. clince a supervisory relay-coil included in circuit between the negative side of the battery and the test-thimbles, when a plug has been inserted within such a thimble there will be a dil'lerence in potential between the test-thimbles oi the busy lit 3 and the tip 01 the calling-plug. The contact of the tip of the plug 26 with a busy thirnbie causes a partial discharge of a condenser 32, thereby producing a click in the operators telephone set.

The resistance i l. is connected between the negative side of the battery 13 and the generator-tcrminal associated with the tip-strand of the cord-circuit. This is to prevent the release ol. the cut-oil relay-armatures 1-1 and 15 upon the interruption oi? the circuit through the coil 12 upon the 111{tlll[)1ll2ttl()tl ot the ringing-key.

it will be seen that in accordance with my invention the coils of the dif'lerential relays are connected in but one 01* the limbs from the commonbattery to the substation apparatus, whereby an unbalancing ot the system due to detective insulation or leakage of any kind does not injuriously 2 llect the proper operation of the cut-oil relay.

Talking-current is supplied to the transmitters at the substations from the battery 13 through a circuit each limb oi which includes an inductive rcsisti'rnce, whereby the short-cin euit ol voice-currents through the common battery is prevented. At the same time the talking-circuit between connected substations is entirely free From inductive re. stances ex cept those of the supervisony relays 3t and E37, serially connected between the sides oi the cord-strand 28, These serially-connected relays 36 and 37 however are connected in par allel with the condenser 33, whereby the transmission of voiceaiaurrents perfected.

While l have herein shown and described one particular embodiment oi my invention, it will be am arent to those skilled in the art that many modifications and changes therein may be mnployed without departing from the spirit thereof. it do not, therefore, wish to limit myself to the precise disclosnm herein set forth; but,

gle limb of said line, a line-signal controlled l by switching apparatus at the substation, and means whereby the connection of the cord connectingapparatus with said line causes an actuation of said relay to destroy the substation control of said line-signal.

2. In a telepholie-exchange systen'l, the combination with a telephoneline extending by its limbs from a substation to an exchange, of cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-ofi relay having two difi'erential windings serially included in a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of the cord connecting apparatus with saidlinc causes an actuation of said relay to destroy the substation control of said line-signal.

3. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying current to the substationtransmitters, cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-off relay having two difierential windings serially included in a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of the cord connecting apparatus with said line causes an actuation of said relay to destroy the substation control of said line-signal.

a. In a telephone-exchange system, the combination with ateley'ihone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying current to the substation-transmitters, cord connecting apparatus for connecting said line with another for conversation, a cut-oli' relay having two diiierential windings normally serially included in an electrical path between one terminal of the source of current and the substation apparatus, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said relay.

In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplyrelay having two ditiercntial windings normally serially ,included in an electrical path between one terminal of the source oi current and the substation apparatus, a line-signal normally serially included in circuit with the telephone-line, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said relay to disconnect said line-signal from the telephone-line.

6. In a telephone-exchange s stem,the combination with a telephone-line extending by its limbs from a substation to an exchange, of

connectingsaid line with another for conversation, a cut-oil relay having two differential windings normally serially included in a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit through a winding of said relay thereby causing an actuation of said relay to disconnect said linesignal from the telephone-line.

7. In a telephone-exchange system,the combination with a telephone-line extending by its limbs from a substation to an exchange, of

connecting said line with another for conversation, a cut-ofi relay having two differential windings serially included in a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit of decreased resistance through a winding of said relay, thereby causing an actuation thereof to destroy the substation control of said line-signal.

8. In a telephone-exchange system,the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying current to the substation-transmitters, cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-off relay having two differential windings normally serially included in a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes through a winding of said relay, thereby cansing an actuation thereof to destroy the substation control of said line-signal.

9. In a telephone-exchange system,the com bination with a telephone-line extending by its g limbs from a substation to an exchange, of a source of current at the exchange forsupplying current to the substation transmitters,

ing current to the substationtransmitters, cord connecting apparatus at the exchange for cord connectingapparatus tor connecting said line with another for conversation, at cutoii' connecting said line with another for conversal tion, a cut-oh relay having two ditderential cord connecting apparatus at the exchange for Y the closure of a circuit of decreased resistance e cord connecting apparatus at the exchange for windings serially included in a single limb oi said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes the closure oi a circuit through a windil'ig oi said relay, thereby causing an actuation oi said relay to disconnectsaid line-signal from the telephoneline.

10. in a telephone-exchange system, the

combination with a tele 'ihone-linc extending relay.

ii. in a telephonc-exchange system, the combination with a telephone-line extending by its limbs from asnbstation to an exchange, oi cord connecting apparatus for connecting said line with another ior conversation, a cutofi relay having two diilerential windings normally serially included in circuit with a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation 0i said relay to destroy the substation control of said lii'lU-Sigi'lill, and to cause the establishment oi a circuit oi low resistance in shunt oi the winding oi said relay.

12. in a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, oi a source of current at the exchange for supplying current to the substatioil-transmitters, cord connecting apparatus for connecting said line with another for conversation a cut-oil relay having two diilereniiial windings normally included in circuit with a single limb oi said line, a line-signal controlled by switching apparatus at the substation, and means whcrelgiy the connection of said cord connecting apparatus with said line causes an actuation oi said relay to disconnect said line-signal from the telephoneline and to cause the closure of a circuit of low resistai'icc in shunt oi one winding oi said relay.

'3. in a telephone-exchange system, the combimltion with a telephone-line extending by its limbs irom a substation to an exchange, oi a source oi current at the exchange ior supplying current to the substation-transmitters, cord connecting apparatus for connecting said line with another for conversation, at cut-oil relay having two dii'lerential windings normall y serially included in circuit with a single limb 01 said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection oi. the cord connecting apparatus with said, line causes an actuation oi said relay to destroy the substation control oi said line-signal and to cause the closure oi a low-resistam:e circuit in shunt of one winding oi said relay.

'14. in a telephone-exchange system, the combination with a telephone-lii'ie extending by its limbs from a substation to an exchange, oi cord connecting apparatus at the exchange for connecting said line with another for con- 'ersation, a cut-oil relay having two differential windings included in circuit with a single limb oi said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of the cord connecting apparatus with said line causes an actuation o i said line-relay to destroy the substation control oi said line-signal and to close a low-resistance circuit in shunt 0i one winding oi said relay.

15. in a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, oi cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-oil relay having two diiierential windings normally included in circuit with a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connecting of said cord connecting apparatus with said line causes the closure oi a circuit oi decreased resistance through a winding oi" said relay, thereby causing an actuation thereoi to destroy the substation control oi said line-signal and to cause the closure oi a low-resistance circuit in shunt oi' the other winding of said relay.

16. in a telephone exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, oi cord connecting apparatus :ior connecting said line with another ior conversation, a cutoi'i' relay having two di'iiercntial windings normally serially included in circuit with a single limb oi said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection oi said cord connecting apparatus with said line causes the closure of a circuit through a winding oi said relay, thereby cai'ising an actuation of said relay to disconnect said line-signal from the telephcme-iinc and to cause the closure oi a low-resistance circuit in shuntoi the other winding oi said relay.

17. in a telephonecxchange system, the combination with a te1ephone-line extending by its limbs from a substation to an exchange, oi a source oi current at the exchange for supplying current to the substation-transmitters, cord connecting amiaratus for connecting said line with another for conversation, a cut-off relay having two differential windings normally included in circuit with a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit of decreased resistance through a winding of said relay, thereby causing an actuation thereof to destroy the substation control of said line-signal and to cause'the closure of a low-resistance circuit in shunt of the other winding of said relay.

18. In a telephoneexchange system, the combination with a telephone'line entending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying current to the substation-transmitters, cord connecting apparatus for counectingsaid line with another for conversation, a cut-off relay having two differential windings normally serially included in circuit with a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit through awinding of said relay, thereby causing an actuation of said relay to disconnect said line-signal from the telephone-line and to cause the closure of a low-resistance circuit in shunt of the other winding of said relay.

19. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-off relay having two differential windings included in circuit with a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit of decreased resistance through a winding of said relay, thereby causing an actuation thereof'to destroy the substation control of said line-signal and to cause the closure of a low-resistance circuit in shunt of the other winding of said relay.

20. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-off relay having two differential windings normally serially included in a single limb of said line, a line signal controlled by switching apparatus at the substation, means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit through a wind ing of said relay thereby causing an actuation of said relay to disconnect said line-signal from the telephone-line, and means upon actuation of said relay for causing the closure of a low-resistance circuit in shunt of the other winding of said relay.

21. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-off relay having two differential windings serially included in a single limb of said line, a line-signal controlled by switching apparatus at the substation, means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit of decreased resistance through a winding of said relay, thereby causing an actuation thereof to destroy the substation control of said line-signal and means upon actuation of said relay for causing the closure of a low-resistance circuit in shunt of the other winding of said relay.

22. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying current to the substation-transmitters, cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-off relay having two differential windings included in circuit with a single limb of said line, a line-signal controlled by switching apparatus at the substation, and means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit through a winding of said relay, thereby causing an actuation of said relay to disconnect said line-signal from the telephone-line and to cause the closure of a low-resistance circuit in shunt of the other winding of said relay.

23. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying current to the substation-transmitters, cord connecting apparatus at the exchange for connecting said line with another for conversation, a cut-off relay having two dilferential windings normally serially included in a single limb of said line, a line-signal controlled by switching apparatus at the substation, means whereby the connection of said cord connecting apparatus with said line causes the closure of a circuit of decreased resistance through a winding of said relay,there by causing an actuation thereof to destroy the substation control of said line-signal, and means upon actuation of said relay for causing the closure of a low-resistance circuit in shunt of the other winding of said relay.

2%. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for sup plying current to the substation-transmitters, cord connecting apparatus at the exchange for connecting said line with another for conversation, a cutol'li' relay having two dil'l'erential wimlings serially included in a single limb oi said line, a line-sigrnil controlled by switching apparatus at the substation. means whereby the connection ol said cord connecting apparatus with said line causes the closure oi a circuit through a winding oi said relay, thereby causing an actuation of said relay to disconnect said line-signal from the telephone-line, and n'ieai'ls upon actuation of said relay for causing the closure of a low-resistance circuit in shunt oi, the other winding oi? said relay.

25. in a telephone-exchange system, the combination with a telephone-line extending from a substation to an exchange, of cord com'iecting apparatus at the exchange for connectil'ig said line with another for conversation, a line-signal normally serially included in circuit with said line, a source of current at the central station adapted to supply current to the substatioii-transmitters, a cut-o'tl relay having two dill'erential windings nor mally serially included in circuit with said line, and means whereby the connection of said cord connecting apparatus with said line may cause an actuation of said relay to close a circuit oi. low resistance in shunt 01'' one 0.1" the windings of said relay.

26. in a telephone-exchange system, the combination with a telephone-line extending from a substation to an exchange, cl. cord connecting apparatus at the exchange for connecting said line with another for conversation, a source ol current at the central station adapted to supply current to the substatioii-transmitters, a line-signal normally serially included in circuit with said line, a cutol'l relay having two windings normally serially included in circuit with said line, and means whereby the connection of said cord connecting apparatus with said line may cause an actuation oi said relay to close a low-re sistance circuit in shunt of one of the windings of said relay.

27. in a telephone-exchange system, the combination with a telimhone-line extending from a substation to an exchange, oi cord connecting apparatus at the exchange for connecting said line with another for conversation, a lii'ie-sigual normally serially included in circuit with said line, a cuto'l'l' relay normally serially included in circuit with said line, and means whereby the connection of said cord comiecting apparatus with said line causes the establishment 01 a substantially short circuit about a wimling of said relay.

525i. lln a telephone-exchange system, the combii'nition with a telephone-line extending from a substation to an exchange, oi. cord connecting apparatus at the exchange for connectsource ol current at the central station adapted to supply cm'rent to the substatioil-transmitany tors, a line-signal normally serially included in circuit with said line, a cut-ell relay normally serially included in circuit with said line, and means whereby the connection of said cord connecting apparatus with said line may cause the establishment of a substantially short circuit about a winding of said cut-oil relay.

52$). in a telephone-exchange system, the combination with a lJOlUPlIOIIG'llHC extending from asubstation to an exchange, oi cord connecting ap nu'atus at the exchange l'or connecting said line with another for conversation, at sourceof current at the central station adapted to supply current to the substation-transmittors, a line-signal normally serially included in circuit with said line, a cut-ol'i relay having two windings normally serially included in circuit with said line, and means whereby the connection of said cord connecting apparatus with said line may cause the establishment oi a substantially short circuit about one oi the windings of said relay.

30. in a telephone-exchange system, the combination with a telephone-line extending from a substation to an exchange, ol cord connccting apparatus at the exchange for connecting said line with another For conversation, a source ol current at the central station adapted to supply current to the substation-transmitters, a line-signal normally serially included in circuit with said line, a cut-ol'ii' relay having two dillferentially-wound coils normally serially included in circuit with said. line, and means whereby the com'iection of said cord connecting apparatus with said line may cause the establislunent of a substantially shortcircuit about one winding of said relay.

3 in a telephone-exchange system, the combination with a central exchange, of a telephone-line leading therefrom to a substation, a cord-circuit at the exchange having one strand normally continuous throliigh a supervisory signal-lamp, a condenser serially included in circuit with said lamp, a source of current at the central exchange having one of its terminals normally connected to said COl'Ll-Siil'iti'itl through said lamp and an armature and adapted to supply current to said lam p upon connection of said cord-circuit with said line. and a superristn'y relay controlling said armature and adapted when energized upon actuation of substation apparatus to disconnect said cord-strand and lamp from said source of current and to elosi a low resistal'ice in shunt of said lamp.

32. in a tclephone-exchange system, the combination with a tele )hone-line extending from a substation to an exchange, of cord connecting :mparatus at the exchange for connecting said line with another For conversation, at source o'l current at the central station adapted mg said line with another for conversation, a to supply current to the sulistation-transmittors, a line-signal normally serially included m circuit with said line, a cut-oil? relay ha vmg &

two windings normally serially included in circuit with said line, and means whereby the connection of said cord connecting apparatus with said line establishes a circuit of decreased resistance through one of said windings, whereby said relay is actuated, the actuation of said relay serving to close a low-resistance circuit in shunt of the other of said windings.

33. In a telephoneexchange system, the combination with a central exchange, of a telephone-line leading therefrom to a substation, a cord-circuit and a source of current at the central exchange, one strand of said cord-circuit being telephonically continuous through a condenser, the other strand being normally continuous serially through two supervisory signal-lamps and a condenser disposed between said lamps, a supervisory relay for each lamp connected between one terminal of said source of current and the first strand, a circuit connecting said terminal with the other strand 1 through the corresponding relayarmature and supervisory lamp, energization of said relays upon actuation of substation apparatus when said cord-circuit is connected with a line causing attraction of the relay-armatures to disconnect said lamps from said source of current and to establish a short circuit about the corresponding lamps.

3st. in a telcphone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying current to the substationtransmitters,

for connecting said line with another for conversation, means whereby the insertion of a plug of said cord connecting apparatus within said jack closes a circuit of decreased resist ance through one winding of said difierential cut-otl relay to cause an actuation thereof, switching means controlled by the actuation of said cut-off relay to open the circuit from a terminal of said source of current through said line-signal to one limb of the line and to connect said limb with the sleeve-contact of the spring-jack and other switching means controlled by the actuation of said cut-otl relay to close a low-resistance circuit in shunt of that winding of said relay connected between the tip-contact of the spring-jack and a limb of the line.

35. In a telephone-exchange system, the

combination with a cord circuit having a strand normally telephonically continuous through a supervisory signal-lamp, of a supervisory relay adapted upon energization to close a low-resistance circuit in shunt of said lamp.

36. In a telephone-exchange system, the combination with a cord-circuit having oneof its strands normally telephonicall y continuous through a supervisory sign al-lam p, of a source of current having one of its terminals nor mally connected to said cord-strand through said lamp, and a supervisory relay adapted upon energization to disconnect said cord strand and lamp from said source of current and to close a low-resistance circuit in shunt of said lamp.

37. in a telephone-exchange system, the combination with a cord circuit having a strand normally telephonically continuous through a supervisory signal-lamp, of a condenser serially included in circuit with said lamp, a source o'l current having one of its terminals normally connected to said cordstrand and adapted to supply current to said supervisory signal-lamp, and a supervisory relay adapt-ed upon energization to disconnect said cord-strand and lamp from said source of current and to close a low-resistance circuit in shunt of said lamp.

38. In a telephone-exclnmge system, the combination with a cord circuit having a strand normally telephonically continuous through a supervisory signal-lamp, of a supervisory relay adapted upon energization to close a short circuit about said lamp.

39. In a telephone-exchange system, the combination with a cord connecting apparatus, of a calling and answering plug therefor, a supervisory lamp for each plug, one strand of said cord-circuit being normally telephonically continuous through said lamps, and a supervisory relay for each lamp, energization of said relays causing a short circuitto be established about the correspondin g supervisory lamp whereby said lamps are removed from the telephone-circuit.

4E0. In a telcphone-- exchange system, the combination with a telephone-line extending by its limbs 'tromasubstationto an exchange, of a source of current at the exchange nor mally connected in bridge of the limbs of the line, cord connecting apparatus at the exchange, a cut-oil relay included in one of the limbs of the line, armatures for said relay, a line-signal normally serially included in the other limb with one of said armatures, and means upon connection of the cord connecting apparatus in said line for disconnecting said line-signal from the line and for establishing a short circuit about part of the cutofl-relay winding.

&1. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange,

reae izl of a source of current at the exchange normally connected in bridge of the limbs of the line, cord connecting apparatus at the central exchange, a cnt-ofl relay having two windings normally included in one limb cl the line, armatures for said relay, and a line-signal serially included in the other limb with one of said armatures, connection of said cord connecting apparatus with said line causing attraction of said armatures to disconnect the line-signal from circuit and to establish a short circuit about one o]? the cut-ol'li-relay windings.

4:2. in a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange normally connected in bridge of a telephone-line, cord connecting apparatus at the exchange, a cut-ofi' relay having two dii'ii'erential windings normally serially included in one limb oi the telephone-line, an armature for said relay, and a spring-jack for said line, one member of said spring-jack being normally connected with one limb of a telephonc-line through one oi? said diifercntial windings, connection of said cord connecting apparatus with said spring-jack causing attraction of said armature by said cut-oil relay to connect said jack member directly with said limb through a short circuit about said relay-winding.

43. In a telephonc-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange normally connected in bridge of the telephoneline, a cut-ell" relay having two dillerential windings normally serially included in one limb of said line,armatures for said relay, a line-signal normally serially included in the other limb with one oi said armatures, a cord connect ing apparatus at the central exchange, and switch-springs associated with said telephoneline, one of said springs beingnormally connected with one limb of the line through one of said differential windings, the other spring being normally disconnected from the other limb ol the line, connection of the cord con necting ap1' aratus with said springs causii'ig el'iergizz'ttion of said cut'oflf relay to attract its armature, whereby said switch-spring directly connected with the line-limb through a short circuit aboutsaid winding, and whereby the line-signal is disconnected from circuit and the other switch-spring connected with the other limb of the line.

in witness whereof lv hereunto subscribe my name this 14th day oi January, A. D. i903.

El.) h'iUN l) LAN 1).

WVitnesses:

LYNN A. iVimimms, l- An'vnr' L. .l-lANsoN. 

